Method of making a grinding tool



Sept. 15, 1959 F. FAHNOE 2,904,418

METHOD QF' MAKING A GRINDING TOOL Filed Feb. 25, 1955 FIG. 4 /f I F/G. 3. /7/4/ /f Zd .A Il --f /L 4;

MM 5MM A/.f ATTORNEYS.

invention relates to ja .grinding 'tool and 'meth-ods 2,904,418 Patented Sept. 15, 1959 ice 2 shown in Figure 2 but subsequent to -the deposition of bonding material on the yabrasive particles;

Figure 4 is aview in perspective, Partially broken away, illustrating 'the manner in which a .precision sleeve is' used to `join the master mold shown in Figure l to a holder;

Figure 5 is a View vin perspective of the holder carrying the layer of abrasive particles after the master mold `has been .removed therefrom;

Figure 6 is a transverse section, greatly enlarged, of

0 the holder illustrated in Figure 5; 'and orproducingsuch tool and "embodies, more specifically,

the production off a grinding tool provided 'with an extremely flat abrasive surface.

vllt .is often 'necessary 'to shape various articles with greatac'curacy by means of high speed grinders such, for example, 'as in 'the 'lapping 'of quartzrglass, cemented 'carbi'il'es, and ceramics such as vvst'eatite- .In these instances, hardabrasive particles `must be "used 'to provide a satisvfactory cutting operation, diamond 'particles being preferred. Past practices employed such particles 'in 'a 'slurry cooperating with a nat 'disc 'but in `this arrangement, the vcutting action is slow because the diamond `partiel- 4are not anchored and therefore fail to 'exerta'ny appreciable .force `to facilitate the .cutting action. Furthermore, *scratching of `the 'work piece v"cannot'be controlled.

'other disadvantage resides in the'factthat `the diamond abrasive, which relatively expensive, 'is'rap'idly Washed away. Attempts to provide a satisfactory grinding tool incorporating very' hard particles 'with a surface "suffilc'fiertlyiiat forthe precision work involved, such liatness l"being measured by an opticaliiia't and held "'to 'a atness specification on .the order of two light bands, have proven unsuccessful. p l Y In 'accordance 'with Jthe 'present invention, a method is provided to `fornra grinding tool having an Vabrasive `s'ur- "faceiliato 'a very degree vto cutvwork'pieces -with the *precision'required "in :the quartz glass'flapping held, for example. This method comprises providing "a `cylindrical layer of bonded abrasive particles on a dat surface Jsup'pfortel*by 'a master torni. "Ihis fonn 'rn-ayj'then be :axially spaced from a holder by a precision sleeve, a preferably irregular surface on the holder being position'el parallel "to the cylindrical 'layer of bonded abrasive smid/es `In-order to jointhe holder'to t'hel'aye'r of abrasive particles, 'an alloy navi-ng a low Jtennperature eo'elieient of ft'herinal expansion and a low melting 'pointrnay be nowed into the 'precision sleeve Vand yvvh'en'it hardens, "the Vmaster mold and holder will `be 'joined 'The 'master mold may then -be stripped from the layer of abrasive particles, 'this 'operation k"'o'ezin'g facilitated if a layer of lubricating agent "is interposed ybetween Vthe abrasive `particles and the mas- Lterrhld, andthe layer of'partic'les etched to better expose the abrasive particles.- lIn this manner, a highly precision f'grindingstool with a cutting surface :ilat to a specification toptwo light bands or'better may be produced.

Theseand further advantages of the presentiinvention ywill lbe ymore 4readily understood when the fol-lowing description is-read in connection with the accompanying drawings in which:

Fi'gure' Il.` isla perspective -view fofla master mold having v'abr'asiive `,particles ydeposited on fa -fat end .'.portiong Figure 2 is "a transverse sect-ion, greatly enlarged, of `'die fm'as'termold shown in Figure l'illus'trating-'the abrasive 7'particlesl deposited lthereon;

Figure 3 is "a sectioneo'f themast'er 'moldsimilar to that hFigure 7 is a transverse .section similar to Figure 6 illustrating the abrasive surface after etching;

Referring in greater detail to an illustrative embodiment of 'the invention with particular 'reference to the drawings, a master mold 10 is formed of 'a cylindrical body 11 coaxially mounting a smaller vdiameter cylindrifcal 'front piece '112 provided wi'th'an extremely flat surface 1-3. lFor example, 'the surfaceis preferably l'held flat to va specification oftwo light 'bands'vvhen measured by means of an optical dat. As shown in Figure 2, 'a layer of a conventional conductive solid lubricant 14, enlarged -for clarity, may be vplaced on the optically flat surface 13, 'abrasive particles 15 being electrophoretic'ally deposited on the layer 14. The conductive solid'lub'ricant layer '14 may comprise graphite, "for example. Of course, it will be understood that the layer 14 is of uniform thickness in order to obtain the benefits of the optically flat surface 13. The size of the particles 15 has `been greatly exaggerated in the drawings 'for the sake of clarity. .It will be understood uthat such abrasive particles Vmay be extremely .small having diameters, 'forexarnple, on the order of 5 to `l0 microns.

As discussed in copending application Serial No. 388,- 119, led October 26, 1953, by Frederick Fahnoe and llames J. 'Shyne, and .now Patent No. 2,858,256, electrophoretic deposition occurs when an electrostatic field is established betweentwo electrodesimm'er'sed within a colloidal or gross 'dispersion of charged particles, thus causing the migration 'of 'the particles comprising the sus- ,pendedphasetoward one of the' electrodes and producing the deposit of "an adherent coating on that electrode. Exceptionl uniformity Yof Acoating'thiekness and coinpacting (with an attendant relatively high coating density) are obtained, as compared with dipping, spraying, brushing, and other .more conventional methods of application.

The deposition itself can be precisely controlled'through closecontrol of the main parameters ofthe electrophoretic process; i.e., the voltage applied between the electrodes, the relative spacing of the vkelectrodes, 'the duration of the .process yand the dispersion concentration. .Although this `precise control can only be obtained within certain 'parameter ranges described in more detail in vcopending application Serial No. 386,882, 'iiled October 19, 1953, by Frederick Fahno'e and I ames I. Shy'ne, in general the rate of deposition increases Iboth with increased voltage and 4increased 'dispersion concentration and decreases with increased electrode spacing. Moreover, the amount of deposition increases as the .period of deposition is increased.

The liquid phase which is the carrier 'for the charged particles in th'e electrophoretic deposition must be a vrelatively anhydrous, non-conductive fluid. By a relatively non-conductive fluid we mean a iiuid having a condfuctivity falling Within the range of l05 to 10*9 ohm-cm., and preferably 'falling within the range of 10-V6 to 10"8 ohm-cm. Examples of this type of fluid are: alcohols lsuch as methyl, ethyl and isopropyl alcohols; ketones suc'h as acetone; esters such as ethyl acetate; `and aromatics such a's nitrobenzene.

The coating formed by the deposition can be composed of any 'abrasive particles capable of being Acolloidally dis- A"'pers'ed. For example, 'any 'natural abrasives such as diamond particles, silicon carbide, emery, garnet and the like, or any manufactured abrasives such as carbides, fused alumina particles and various metallic compounds, or mixtures of these abrasives can be so dispersed. The colloidal dispersion need not be stable as long as the charged particles can be retained in dispersion through forced agitation or by the use of peptizing agents; such particles may have diameters falling within the range 1A00 to 100 microns.

Subsequent to the deposition of the porous layer of abrasive particles on the layer 14, a layer of metal 16 is preferably electrolytically deposited on theconductive layer 14 through the interstices between the particles 15, such deposition continuing until the metal 16 covers the particles 15 as shown in Figure 3. This process effec4 tively bonds the abrasive particles 15 together to form a bonded layer 17 that may readily be removed from the mold 10 due to the lubricant layer 14.

More particularly, when electrolytic deposition is employed, the bonding material 16 must be a metal or alloy which is capable of being electrolytically deposited; for example, chromium, nickel, silver, copper or cobalt. In this situation, the bond is formed through mechanical meshing of the bonding and base materials at their com mon surface.

When electroless deposition is employed, the bonding material must be chosen from a small class of metallic compounds which are capable of being reduced to metal on the surface of the base material in the presence of a catalyst and without the application of heat; examples of this class are cobalt and nickel.

The deposition of the removable layer of bonded abrasive particles on the conductive layer 14 may be in accordance with the principles disclosed in copending application Serial No. 386,882, tiled October 19, 1953, by Frederick Fahnoe and James I. Shyne, and now Patent No. 2,848,391.

Referring next to Figure 4, the master mold 10 carrying the layer of bonded abrasive particles 17 coaxially fits into one end of a precision formed preferably cylindrical sleeve 18, the outer diameter of the cylindrical piece 12 matching the inner diameter of the sleeve 18. Preferably, the interior surface of the sleeve 18 carries a layer 19 of a conventional release or lubricating agent such as a silicon containing oil. Extending longitudinally from the other end of the sleeve 18 is a port 20 adapted to receive a flow of molten metal.

Positioned in the other end of the precision sleeve 18 is a holder 21, best shown in Figure 5, formed of a cylindrical body piece 22 and a cylindrical joining piece 23 mounted coaxially therewith. Preferably, an outer at surface 24 of the piece 23 is provided with suitable irregularities formed by knurling, serrating, scoring, or like processes. rl`he outer diameter of the joining piece 23 preferably matches the inner diameter of the sleeve 18 to permit a close fit therebetween, as shown in Figure 4.

With the master mold 10 and the holder 21 mounted in the sleeve 18 as shown in Figure 4, an alloy 25 having a low temperature coeicient of thermal expansion is poured through the port into the sleeve 18 to ll the space between the layer 17 and surface 24 which are maintained in a parallel relation. The alloy 25 must, of course, have the property of securely adhering to the metal from which the holder 21 is formed and the metal employed as the bonding agent 16. In addition, the alloy 25 should have a fairly low melting point in order to preclude the warpage of any of the elements involved in the process by exposure to excessive heat. For example, the alloy commercially designated Cerrotru, consisting of 58% bismuth, 42% tin and having a melting point of about 138 C. and a low coecient of thermal expansion. Another similar alloy is Cerromatrix, which contains 14.5% tin, 48% bismuth, 28.5% lead and 9% antimony, with a melting point of about 105 C.

After the sleeve 18 has been filled with the alloy 25, it

is allowed to cool and harden or it may be artificially cooled in any desired manner. When the alloy 25 has firmly set, the master mold is stripped from the bonded adhesive particle layer 17, this operation being facilitated by the solid conductive lubricant 14. Subsequently, the holder 21, which with the attached cylinder of hardened alloy 25 and bonded layer 17 forms a grinding tool, is removed from the sleeve 18. The irregular surface 24 aids in securely bonding the alloy 25 to the holder 21.` The removal of the grinding tool from the sleeve 18 does not present any diiculties due to the use of the lubricating layer 19. Also, since the port 20 extends from the end of the sleeve 18, any of the alloy 25 protruding therethrough will not interfere with the removal of the grinding tool.

In Figures 5 and 6 the grinding tool is illustrated immediately after its removal from the sleeve 18. In certain instances, it may be used as shown when, for example, the bonding metal 16 is fairly soft and normal grinding use will wear it away from the particles 15. However, in many instances it is desirable to etch the layer 17 in order to better expose the abrasive particles 15. For example, the layer 17 may be electrolytically etched to provide the configuration shown in Figure 7 in which the abrasive particles 15 extend somewhat above the bonding metal 16. At this time, the grinding tool is readied for insertion into a suitable chuck for use in precision lapping of various articles.

A grinding tool formed in accordance with the methods described above has an abrasive surface defined by the particles 15 which has an optically flat surface, i.e., a surface flat when measured optically which is substantially as flat as the optically at surface 13 upon which it is formed. Furthermore, the use of the precision sleeve 18 accurately positions the cutting surface of the grinding tool parallel to the holder 21. Such a grinding tool permits extremely high precision work and since the abrasive particles 15 are securely anchored, scratching is highly controlled and the cutting speed is impressively increased.

It will be understood that the above-described embodiments of the invention are illustrative only and modifications thereof will occur to those skilled in the art. Therefore, the invention is not to be limited to the specific apparatus disclosed herein but is to be defined by the appended claims.

I claim:

1. A method of forming a grinding tool comprising the steps of providing a removable cylindrical layer of bonded abrasive particles on an extremely at surface supported by a master element, axially spacing a circular surface on a holding member from the cylindrical layer on the master element with the surface and the layer facing each other, owing a molten alloy into the space between the master element and member to join the cylindrical layer of bonded abrasive particles to the holding member when the molten metal hardens, and removing the master element from the cylindrical layer of bonded material.

2. A method as defined in claim 1 which comprises the additional step of etching the cylindrical layer of bonded abrasive particles after removal of the master element to better expose an abrasive surface.

3. A method of forming a grinding tool comprising the steps of providing a removable cylindrical layer of bonded abrasive particles on an optically flat surface supported by a master element, positioning a hollow open ended figure of revolution to axially space a circular surface on a holding member from the cylindrical layer on the master element with the surface and the layer facing each other, filling the figure of revolution with a molten alloy to join the cylindrical layer of bonded abrasive particles to the holding member when the molten alloy hardens, removing the master element from the cylindrical layer of bonded material, and removing the holding member from the figure of revolution.

4. A method as dened in claim 3 which comprises the additional step of etching the cylindrical layer of bonded abrasive particles after removal of the master element to better expose an abrasive surface.

5. A method of forming a grinding tool comprising the steps of providing a removable cylindrical layer of bonded abrasive particles on an optically ilat surface supported by a master element, coaxially positioning a cylindrical sleeve having an inner diameter equal to the outer diameter of the cylindrical layer of bonded abrasive particles in overlapping relation with the cylindrical layer, coaxially positioning a cylindrical portion of a holding member in the other end of the sleeve With its surface facing the layer of bonded abrasive particles, lling the sleeve with a molten alloy having a low melting point and a low temperature coeicient of thermal expansion to join the cylindrical layer and the holding member when the molten alloy hardens, removing the master element from the cylindrical layer of bonded material, and removing the holding member from the sleeve.

6. A method as dened in claim 5 which comprises the additional step of etching the cylindrical layer of bonded abrasive particles after removal of the master element to better expose an abrasive surface.

7. A method as defined in claim 5 in which the the interior surface of the sleeve is coated with a lubricating release agent prior to the steps of mounting the master element and the holding member therein.

8. A method as defined in claim 5 in which the cylindrical layer of bonded abrasive particles is formed by electrophoretically depositing abrasive particles on an optically ilat surface, and electrolytically depositing metal on the flat surface between the particles to bond them together.

9. A method as defined in claim 5 in Which irregulan'- ties are formed on the surface of the holding member prior to positioning it in the sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 704,399 Taluau July 8, 1902 1,151,317 Wood Aug. 24, 1915 2,367,286 Keeleric Jan. 16, 1945 2,388,020 suwa oct. 30, 1945 2,423,293 Ciell July 1, 1947 2,467,596 Pratt Apr. 19, 1949 2,496,352 Metzger et al. Feb. 7, 1950 2,728,124 Soiield Dec. 27, 1955 UNITED STATES PATENT OFFICE FECATE 0F C0 ECTION Patent No., 2,9049418 September l5, 1959 Frederick Falncj@ It is hereby 'certified that errar .appears in the ,above nlmbered patent requiring correction and phat the aid Lair-)nrs Patent should read as @erreur-ed belcnzvo In the'. grant, lines 2 and 3.22 and in chel heading no the printed speification, lines 3 and 4, name' `of asigneef, for "Vibro Corporation of America read um Vitra Corporation o America wo Signed and Sealed this 19th day of April 1%() (SEAL) Atest:

KARL E., AXLTNE ROBERT C. WATSON Attesfting Officer I Conmissioner of Patent-:s 

1. A METHOD OF FORMING A GRINDING TOOL COMPRISING THE STEPS OF PROVIDING A REMOVABLE CYLINDRICAL LAYER OF BONDED ABRASIVE PARTICLES ON AN EXTREMELY FLAT SURFACE SUPPORTED BY A MASTER ELEMENT, AXIALLY SPACING A CIRCULAR SURFACE ON A HOLDING MEMBER FROM THE CYLINDRICAL LAYER ON THE MASTER ELEMENT WITH THE SURFACE AND THE LAYER FACING EACH OTHER, FLOWING A MOLTEN ALLOY INTO THE SPACE BETWEEN THE MASTER ELEMENT AND MEMBER TO JOIN THE CYLINDRICAL LAYER OF BONDED ABRASIVE PARTICLES TO THE HOLDING MEMBER WHEN THE MOLTEN METAL HARDENS, AND REMOVING THE MASTER ELEMENT FROM THE CYLINDRICAL LAYER OF BONDED MATERIAL. 